There have been conventionally proposed various methods for determining whether or not knocking (knock) occurs. A knock controller for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2003-21032 includes: a knock sensor for detecting knocking in an internal combustion engine; a statistical processor for statistically processing an output signal detected by the knock sensor; a first temporary determiner for determining occurrence of knocking based on a result processed by the statistical processor; a second temporary determiner for determining occurrence of knocking based on a waveform of the output signal detected by the knock sensor; and a final knock determiner for finally determining occurrence of knocking based on the results of the knock temporary determination by the first temporary determiner and the knock temporary determination by the second temporary determiner. When both of the first and second temporary determiners determine that knocking occurs, the final knock determiner finally determines that the knocking occurs.
By the use of a knock temporary determination in accordance with a statistically processing program and a knock temporary determination in accordance with a waveform program, the knock controller disclosed in Japanese Patent Laying-Open No. 2003-21032 finally determines that the knocking occurs only when both of the temporary determinations result in that the knocking occurs. As a consequence, the occurrence of the knocking can be accurately determined in spite of an output signal resulting from the erroneous detection of the knocking by the knock determination by the use of only the statistically processing program or the waveform program.
Meanwhile, besides vibrations caused by the knocking, vibrations may be caused by the seating of an intake valve or an exhaust valve in the internal combustion engine. Otherwise, vibrations may be caused by actuation of an injector (in particular, a direct injector for directly injecting fuel into a cylinder) or a high-pressure pump for supplying fuel to an injector. When such vibrations are detected as noises together with the vibrations caused by the knocking, a waveform different from that during the knocking is detected irrespective of the occurrence of the knocking. Alternatively, a waveform similar to that during the knocking is detected even without any occurrence of the knocking. In this case, when the occurrence of the knocking is determined based on the waveform, like in the knock controller disclosed in Japanese Patent Laying-Open No. 2003-21032, it may be erroneously determined that no knocking occurs irrespective of the occurrence of the knocking, or to the contrary, it may be erroneously determined that the knocking occurs irrespective of no occurrence of the knocking.